I'm not sure how Patreon will explain things to their creators, but no matter what the effect will be similar; about 30% less income for Patreon and creators alike.
According to App Store rules, you're not allowed to disclose the App Store fee to users. So Patreon is not allowed to explain to users that 30% is going to Apple, nor to explain that there are other options. I'm not sure if Apple regulates messaging to creators as well.
According to App Store rules, you're not allowed to disclose the App Store fee to users. So Patreon is not allowed to explain to users that 30% is going to Apple, nor to explain that there are other options. I'm not sure if Apple regulates messaging to creators as well.